Breeding Indian mustard [Brassica juncea (L.) Czern.] for cold-pressed, edible oil production—a review

Indian mustard [Brassica juncea (L.) Czern.] is a more productive oilseed than canola (B. napus L.) in hot regions of Russia, India, China, and Canada with somewhat unreliable rainfalls, whereas canola is the higher yielding species in more temperate, wetter regions. The specific agronomic features of the species, and their performance in various Australian regions are reviewed. The discovery of the genes for low erucic acid oil production in the seeds of Indian mustard began the conversion of this ancient crop to a canola-type oilseed for dry areas. Initially, many accessions were field-tested at Wagga Wagga and Canberra, but 2 seed-borne diseases, leaf and stem blight and seed rot, were destructive. Accessions from South Asia were severely damaged by the blight caused by Pseudomonas syringae pv. maculicola Young, Dye & Wilkie 1978, whereas most of the cultivars from latitudes above 45°N were resistant. A phytotron procedure was developed for screening seedlings. The segregation pattern in F2 families from resistant × susceptible crosses suggested that reactions to a typical Pseudomonas isolate were controlled largely by co-dominant resistance (PsmR ) and susceptibility (PsmS ) alleles at one locus. F3 families with field resistance equal to the PsmR/PsmR parents were readily recovered, indicating that few or no modifying genes affected disease reactions. Resistant families selected from each of 6 crosses yielded 13.8% more seed (P < 0.001) than the corresponding segregating and susceptible families when these were tested at Canberra and Wagga Wagga. The disease became unimportant when most entries in field trials were resistant. A seed-rotting disease caused by a yeast with distinctive ascospores closely resembling those of Nematospora sinecauda Holley, Allan-Wotjas & Phipps-Todd 1984 occurred in some imported and locally grown seed samples, but was eliminated by hot water treatment of seed prior to sowing and by control of the presumed insect vector, Nysius vinitor (Bergroth), during seed maturation in the field. No previous record of the occurrence of this disease in Australia was found in the literature by a plant pathologist. The availability of breeding lines with low erucic acid seed oil, Pseudomonas resistance, and a predominance of propenyl glucosinolate in the meal permitted the development of a cold-pressed, edible oil industry by a family company (Yandilla Mustard Oil Enterprise) at Wallendbeen, NSW. The original oil has a mild nutty flavour, but now a larger proportion of the market requires a pungent, mustard-flavoured oil containing a trace of propenyl isothiocyanate, the hydrolytic product of the corresponding glucosinolate in the meal. The full-flavoured meal is sold for table mustard and pickle manufacture, as a stock feed ingredient containing approximately 30% protein and 18% oil, and for the distillation, by another small company at Cowra, NSW, of propenyl isothiocyanate, which is used as a flavouring and preservative in food, especially in Japan. This review describes the breeding of cultivars for cold-pressed oil production, as an off-shoot of the canola-grade B. juncea project. Five successively improved, Pseudomonas-resistant cultivars were developed by crossing and pedigree selection for higher yield under a range of limiting conditions, and released for cold-pressed, low erucic acid oil production. The rate of yield increase in the cultivars released between 1989 and 2001 was 2.4% per annum as judged from small plot yields of all cultivars in each of 4 years at Wallendbeen. Flowering time adjustment provided a one-off improvement, but continued progress seems possible by field selection for traits such as increased resistance to the Sclerotinia and Alternaria pathogens, resistance to acid soils, waterlogging, frost at flowering, heat and drought during seed maturation, and increased efficiency of nutrient utilisation. The nutraceutical properties of mustard oil, and the chemical differences among current B. juncea seed products, are described. Possible future developments are discussed.